Conventional polyamide curing agents for use in surface coatings and adhesives are generally prepared by the reaction of a diamine with a mono- or di-carboxylic acid (such as a long chain unsaturated fatty acid or a derivative thereof) in such manner as to create a polymeric molecule that is amine-terminated and contains amine moieties capable of reacting with an epoxy resin at ambient or elevated temperatures.
Examples of such conventional polyamide curing agents can be found in:
U.S. Pat. No. 5,319,062, which teaches a polyamide condensation reaction product between an alkylene polyamine having between 4-20 carbon atoms and dimeric acid mixture containing at least 50% by weight of a non-cyclic dimeric acid or alkyl ester thereof;
U.S. Pat. No. 5,948,881, which discloses an amine-terminated polyamide formed from fatty mono-acids, dimer acids, polyethylene polyamines and piperazine ring containing polyamines;
U.S. Pat. No. 6,111,030, which teaches a solid amine-terminated polyamide curing agent prepared by reacting an excess of a polyamine compound with a dicarboxylic acid where the ratio of equivalents of amine to acid groups 1.05:1 to no greater than 1.95:1;
U.S. Pat. No. 6,500,912, which discloses a liquid amine-terminated polyamide curing agent obtained from C18-C30 dicarboxylic acids and di- or polyamines;
U.S. Pat. Nos. 7,655,736 and 8,293,863, which describe a curing agent composition formed by reacting a multifunctional amine with a dimer fatty acid and where the curing agent may contain at least 15 mole % tetrahydropyrimidine-containing components; and
U.S. Pat. Publ. No. 2012/0190799, which teaches a curing agent composition formed by reacting a multifunctional amine with a dimer acid and carboxylic monoacid and where the composition is free from tetrahydropyrimidine-containing components and piperazine-containing compounds.
While conventional polyamide curing agents provide many benefits including one or more of ease of use, low toxicity, cost efficiency, long working time or pot life, good adhesion, blush resistance, flexibility, and resistance to water, their disadvantages serve to limit their utility in certain cases. For instance, when used in curing epoxy resins at low temperature (for e.g. less than 10° C.), the curing reaction occurs over a long period of time and produces coatings having poor chemical resistance, a low glass transition temperature, poor heat resistance and low hardness. It is therefore an object of the present disclosure to provide a novel multifunctional polyamide curing agent that provides the beneficial properties exhibited by conventional polyamide curing agents while reducing the extent of their limitations.